Background and objectives: Low level laser therapy (LLLT) has been demonstrated to modulate inflammatory processes with evidence suggesting that treatment protocol, such as wavelength, total energy, and number of treatments determine the clinical efficacy.

In this study, the effects of LLLT mediated by different wavelengths and continuous versus pulsed delivery mode were quantified in a transgenic murine model with the luciferase gene under control of the inducible nitric oxide synthase (iNOS) expression.

Study design/material and methods: LLLT modulated iNOS gene expressed in the acute Zymosan-induced inflammation model is quantified using transgenic mice (FVB/N-Tg(iNOS-luc)). Here, an energy density of 5 J cm-2 at either 635, 660, 690, and 905nm in continuous wave mode and at 905 nm for short pulse delivery were evaluated.

Age of the animals was determined as additionally modulating the inflammatory response and the LLLT efficacy for some treatment protocols.

Results: Animals younger than 15 weeks showed mostly a reduction of iNOS expression, while older animals showed increased iNOS expression for some LLLT protocols. Intensity and time course of inducible nitric oxide expression was found to not only depend on wavelength but also on the mode of delivery, continuous versus pulsed irradiation.

Discussion: Pulsed delivery of 905 nm radiation showed higher signal in both age groups. LLLT mediated by 690 nm significantly reduced the BLI signal compared to control groups for both age groups, indicating an effect on iNOS expression.

Mitochondria and the rough endoplasmic reticulum both have high relative amounts of lipid membrane shown to absorb NIR light and their size and possibility of lipid as being the main absorber makes both organelles potential target structures for selective photothermolysis mediated LLLT; wherein, the mechanism is possible due to change in the membranes integrity over time periods less than a few microseconds but long enough to permit ions or proteins to cross them.

Additionally, for the pulsed light model, the bioluminescence intensity (BLI) signal peaked at a later time (four to six hours after) compared to other groups (Figure 1).

Furthermore, a 700 percent increase in nitric oxide production over control was observed when using 905 nm pulsed delivery (Figure 2).

Of additional clinical importance is the efficacy of the 905 nm NIR light as it experiences a lower attenuation compared to 635 nm red light and hence is better suited for the treatment of large tissue volumes such as knee joints affected by osteoarthritis.

Conclusion: LLLT exhibits different effects in induced inflammatory process according to different wavelengths and wave mode. Upregulation of iNOS gene following 905nm pulsed wave suggests a different mechanism in activating the inflammatory pathway response when compared to the continuous wave.